1. Field of the Disclosure
The present disclosure relates generally to a method of handling an ATTACH reject message at a user equipment (UE), and more particularly, to a method of handling an ATTACH reject message with #14 cause at the UE.
2. Description of the Related Art
Generally, a user equipment (UE) must register with a network to receive one or more services that require registration such as “Network Attachment.” The UE triggers an ATTACH request to the network and the network either accepts or rejects the ATTACH request after checking whether all associated subscriptions are available for the services for which the UE is trying to register. If all of the associated subscriptions are available then the network replies with an ATTACH accept message, otherwise it replies with an ATTACH reject message and also indicates a cause for rejecting the service request from the UE. One such reject cause is general packet radio service (GPRS) mobility management (GMM) reject cause number 14 (e.g. #14) i.e., evolved packet system (EPS)/general packet radio services (GPRS) services not allowed in a public land mobile network (PLMN), which is used when the UE tries to register for packet switched (PS) services in the network but the UE is not subscribed to use the PS services in the network.
Further, the third generation partnership project (3GPP) system currently has two issues handling a reject cause #14 in a long term evolution (LTE) system, a second generation (2G) system, or a third generation (3G) system. The issues are as follows:
a) 3GPP specification 24.301 does not consider the scenario where an evolved universal terrestrial radio access (E-UTRA) is disabled due to reject cause #14 “No EPS services in this PLMN” and the GPRS services are enabled after manual selection of the PLMN.
b) 3GPP specification 24.008 does not consider the handling of reject cause #14 “No GPRS services in this PLMN” for the UEs using a subscriber identity module (SIM) type (which does not contain user preferred and operator preferred PLMN lists).
In a conventional system and method, as shown in FIG. 1A, when a UE is rejected with evolved packet system (EPS) mobility management (EMM) cause #14 “EPS services not allowed in this PLMN,” the E-UTRA is disabled as per clause 4.5. 3GPP specification 24.301 discloses the following:                #14 (EPS services not allowed in this PLMN)                    The UE shall set the EPS update status to EU3 ROAMING NOT ALLOWED (and shall store it according to sub clause 5.1.3.3) and shall delete any Globally Unique Temporary Identifier (GUTI), last visited registered TAI and eKSI. Additionally, the UE shall reset the ATTACH Attempt counter and enter the state EMM-DEREGISTERED.PLMN-SEARCH. Further, the UE shall store the PLMN identity in the “forbidden PLMNs for GPRS service” list.            The UE operating in Circuit Switched (CS)/PS mode-1 or CS/PS mode-2 of operation which is already International Mobile Subscriber Identity (IMSI) attached for non-EPS services is still IMSI attached for the non-EPS services and shall set the update status to U2 NOT UPDATED.            The UE operating in the CS/PS mode-1 of operation and supporting A/Gb or Iu mode may select GSM EDGE Radio Access Network (GERAN) or Universal Terrestrial Radio Access Network (UTRAN) radio access technology and proceed with the appropriate Mobility Management (MM) specific procedure according to the MM service state. In this case, the UE shall disable the E-UTRA capability (see sub clause 4.5).            The UE operating in CS/PS mode-1 of operation and supporting A/Gb or Iu mode may perform a PLMN selection according to 3GPP TS 23.122 [6].            The UE operating in CS/PS mode-1 of operation and supporting S1 mode only, or operating in CS/PS mode-2 of operation shall delete the list of equivalent PLMNs and shall perform the PLMN selection according to 3GPP TS 23.122 [6].            If A/Gb mode or Iu mode is supported by the UE, the UE shall in addition handle the GMM parameters GMM state, GPRS update status, P-TMSI, P-TMSI signature, RAI, GPRS ciphering key sequence number and GPRS attach attempt counter as specified in 3GPP TS 24.008 [13] for the case when the combined attach procedure is rejected with the GMM cause with the same value.                        
Further, as per 3GPP specification 24.301, enabling of the EUTRA for this reject is possible only through power off/on or SIM/USIM removal. 3GPP specification 24.301 discloses the following:                4.5 Disabling and re-enabling of UE's E-UTRA capability                    If the E-UTRA capability was disabled due to receipt of EMM cause #14 “EPS services not allowed in this PLMN”, then the UE shall enable the E-UTRA capability when the UE powers off and powers on again or the USIM is removed.                        
Further, the 3GPP does not consider the issue below:                The User can manually select the #14 rejected PLMN, in such case UE has to try registration for PS services on this PLMN.        If GPRS/EPS service registration is accepted, PLMN gets removed from the “forbidden PLMNs for GPRS service” list but EUTRA still remains disabled which leads to no access to LTE.        This will cause problem to user as high data throughput, IMS, VoLTE feature available on LTE are not provided and UE will remain on legacy RATs.        
In a conventional system and method, as shown in the FIG. 1B, the 3GPP specification does not consider #14 reject handling when the UE is using the SIM/USIM that does not contain the files “User Controlled PLMN Selector with Access Technology,” “Operator Controlled PLMN Selector with Access Technology,” but only contains the “PLMN Selector” data file. 3GPP specification 24.008 discloses the following:                #14 (GPRS services not allowed in this PLMN)                    The UE shall delete any RAI, P-TMSI, P-TMSI signature, and GPRS ciphering key sequence number stored, shall set the GPRS update status to GU3 ROAMING NOT ALLOWED (and shall store it according to sub clause 4.1.3.2), shall reset the GPRS attach attempt counter and shall change to state the GMM-DEREGISTERED.            The UE shall store the PLMN identity in the “forbidden PLMNs for GPRS service” list.            As an implementation option, a GPRS UE operating in operation mode A or B may perform the PLMN selection according to 3GPP TS 23.122 [14].            If the UE in GAN mode performs the PLMN selection, it shall request the PLMN list in the GAN (see 3GPP TS 44.318 [76b]) prior to performing the PLMN selection from this list according to 3GPP TS 23.122 [14].            The UE shall not perform the optional PLMN selection in the case where the PLMN providing this reject cause is:            On the “User Controlled PLMN Selector with Access Technology” or,            On the “Operator Controlled PLMN Selector with Access Technology” list or,            The PLMN identified as equivalent to any PLMN, within the same country, contained in the lists above.                        
Further, when #14 reject is encountered on the PLMN present in a “PLMN Selector” data file, a UE will perform the PLMN selection causing a CS paging miss, data stall, and no service issues. The UE may come back to the same PLMN after traversing the complete available PLMN list and attempting to register each one in the PLMN list.
In a conventional system and method, as shown in the FIG. 1C, the 3GPP specification does not consider #14 reject cause handling when a UE is using a SIM/USIM that contains “User Controlled PLMN Selector with Access Technology” and “Operator Controlled PLMN Selector with Access Technology” data files with the corresponding access technology not being part of the operating mode. 3GPP specification 24.008 discloses the following:                #14 (GPRS services not allowed in this PLMN)                    The UE shall delete any RAI, P-TMSI, P-TMSI signature, and GPRS ciphering key sequence number stored, shall set the GPRS update status to GU3 ROAMING NOT ALLOWED (and shall store it according to sub clause 4.1.3.2), shall reset the GPRS attach attempt counter and shall change to state GMM-DEREGISTERED.            The UE shall store the PLMN identity in the “forbidden PLMNs for GPRS service” list.            As an implementation option, the GPRS UE operating in operation mode A or B may perform the PLMN selection according to 3GPP TS 23.122 [14].            If the UE in the GAN mode performs the PLMN selection, it shall request the PLMN list in the GAN (see 3GPP TS 44.318 [76b]) prior to performing the PLMN selection from this list according to 3GPP TS 23.122 [14].            The UE shall not perform the optional PLMN selection in the case where the PLMN providing this reject cause is:            On the “User Controlled PLMN Selector with Access Technology” or,            On the “Operator Controlled PLMN Selector with Access Technology” list or,            A PLMN identified as equivalent to any PLMN, within the same country, contained in the lists above.                        
Further, when a #14 rejection is encountered on a PLMN available in a selector list, and an SIM/universal SIM (USIM) contains a “User Preferred PLMN” list and “Operator preferred PLMN” list, but its access technology is not part of a UE's radio access technology (RAT) mode. For example, if a UE is operating in an LTE-Universal Mobile Telecommunications System (UMTS) mode, but the SIM/USIM has a “User Preferred PLMN” list and an “Operator preferred PLMN” list with global system for mobile communications (GSM) access technology only. In this case, the UE will perform the PLMN selection causing a circuit switched (CS) paging miss, a data stall, and no service issues. The UE may come back to the same PLMN after traversing the complete available PLMN list and attempting to register each one in the PLMN list.